In the field of material classification, it has been considered to classify material through the use of so-called bidirectional reflectance distribution function (BRDF). In this approach, the object is illuminated from multiple different angles by multiple different light sources arranged in a hemispherical dome around the object, and reflected light from each light source is measured so as to form the BRDF, whereafter feature vectors are derived and the unknown material from which the object is fabricated is classified.
It has also been considered to include the notion of spectral BRDF, in which each light source is formed from six (6) differently-colored LEDs, so as to permit spectral tuning of each light source, thereby to differentiate between different materials with increased accuracy.